Some electrically assisted vehicles that control driving force of a vehicle by driving a motor using an electric power of a battery use a technique for extending an assisted running distance by providing a sensor for a brake lever and causing the motor to perform regeneration when detecting, by the sensor, a brake operation by a rider to collect kinetic energy of the vehicle to the battery.
More specifically, there is a technique for making a regeneration amount in case where only the brake operation of either of brake levers is made less than a regeneration amount in case where the brake operations of both brake levers are made. With this technique, it is possible to select either of a larger regenerative braking force and a smaller regenerative braking force by the brake operation or operations with a simple configuration and a low cost, however, the rider has to determine the timing when the regeneration is performed. In addition, the relatively large regenerative braking force is set because of the consistency with the fact that the rider intentionally performed the brake operation. Therefore, the regenerative braking operation of this technique runs off the optimum regenerative braking operation, which corresponds to the running state, an energy amount obtained by the regeneration decreases, and it is impossible to extend the running distance.
Moreover, there is also a technique for changing an effect of the regenerative braking according to an operation amount of the brake. In this technique, the control is performed so as to obtain a regeneration amount according to a vehicle speed, in other words, a larger regeneration amount on a lower speed side. Then, in the running state such as the running in the urban in which the brake operations are frequently performed and the sudden brake operation is easily made, the large regenerative braking force is made and it is possible to frequently charge the battery by the electric current obtained by the regeneration. In addition, it is disclosed that both of the comfortable running and change of the battery can also be performed by the regenerative braking without any brake operation when running on a downhill road. However, in the control that the running on the downhill road is simply determined and the regeneration is performed when no pedal torque exists, too large regenerative braking force is made in a state where the running is performed on the downhill road whose slope is not so large while receiving a head wind, and the rider may have to perform an extra work for keeping the speed. Moreover, because the regeneration brake force in this technique is a function of a fixed speed. Therefore, even when the stable speed is different depending on the degree of the slope and the rider would like to roughly maintain an arbitrary speed, it is necessary to perform diligent actions such as pedalling and braking.
Furthermore, there is a technique for estimating inclination resistance g(θ) {=human power driving force+motor driving force−acceleration resistance (=acceleration*total mass)−other resistances}, and exerting a regeneration brake force for cancelling the inclination, which corresponds to the inclination resistance. In this technique, the inclination resistance is calculated using the total mass, however, the total mass is unknown. Therefore, an estimated mass is actually used. In addition, other frictional resistances, which are proportional to the speed, a constant frictional resistance, air resistance and the like are also unknown. Therefore, due to a difference with the actual mass and errors of other resistances, the inclination resistance g(θ) obtained by subtracting them has a large error. In other words, the inclination resistance has an offset by the errors regardless of the large or small inclination. Then, especially in case of the small inclination, the very large error occurs, and the boundary between the uphill road and the downhill road is largely shifted. As a result, very unnatural behaviors, which are contrary to the purpose of the original assist operation and are very different from the rider's intention, are observed, such as the automatic regenerative brake does not work even in case of the downhill road, and reversely, even in case of the uphill road, the automatic regenerative brake works so that the rider has to pedal with a large power.
As described above, it is difficult for the conventional techniques to perform the regeneration in conformity with the rider's intention when the regeneration is automatically performed without any rider's effort.